Alleged 9/11 terror attacks mastermind Khalid Sheikh Mohammed will stand trial in June 2028, more than a quarter of a century after what the US government has called “the most egregious criminal act on American soil in modern history”.

A military judge ruled the trial would start in two years because a 2027 date sought by prosecutors was too soon.

Mohammed had reached a plea deal where he would admit guilt in exchange for avoiding a death-penalty trial, but a federal appeals court threw out the agreement last summer. Arrested in 2003, he has been held at Guantanamo Bay since September 2006.

Mohammed has previously said he planned 2001’s “9/11 operation from A-to-Z”.

US Air Force judge Lt Col Michael A Schrama ruled on Wednesday that the trial for Mohammed and three co-accused would start on 5 June, 2028.

Alleged accomplices Walid bin Attash, Ali Abdul Aziz Ali and Mustafa al-Hawsawi were listed in the court document.

The start date allowed for additional time to deal with matters of the court, such as resolving any disputes about what evidence can be presented, the judge wrote.

Next month will mark 25 years since hijackers flew planes into the World Trade Center in New York City and the Pentagon in Virginia, while another flight they hijacked crashed in a field in Pennsylvania. About 3,000 people died in the attacks.

Mohammed is accused of conceiving the idea of training pilots to fly commercial planes into buildings and taking those plans to Osama Bin Laden, leader of al-Qaeda.

Mohammed, a US-educated engineer, was captured along with al-Hawsawi in Pakistan in March 2003.

The rejected plea deal, which would have given Mohammed a life sentence without possibility of parole, was reached after two years of negotiation and signed by an official appointed by then-Defence Secretary Lloyd Austin.

But Austin was reportedly caught by surprise, and immediately attempted to revoke it.

The military prison in Guantanamo Bay opened six months after the attacks.

About 15 prisoners are still detained there.